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Chapter 30. VoIP

Voice over IP (VoIP) has been the biggest thing to happen to network
since IP itself. Maybe that’s a stretch, but there’s no denying the way VoIP
has become a big deal for networking folks. So let’s see what’s involved,
how it all works, and how to build a small phone system using a router, a
switch, and some IP phones.

I’ll be using Cisco gear for this chapter, just like all the others.
Sure, there are other solutions out there, but chances are, if you’re
reading this book, you’ll be at a Cisco shop or studying for a Cisco exam,
so Cisco is what I’m using. If you’re hell-bent on not using Cisco (and
there are many execs who feel this way, especially when it comes to
telephony), I recommend you check out the open source Asterisk project.
Using SIP phones (read on to learn about SIP) and a Linux server, you can
build a powerful phone system for little money. There’s even an O’Reilly book to help
you out: Asterisk: The Future of Telephony, Second
Edition, by Jim Van Meggelen et al. (http://oreilly.com/catalog/9780596009625/).

VoIP is a huge topic, and there are entire books devoted to its use
and configuration. As always, my goal here is to get you started, show you
how it works, and provide a real-world example. This chapter will not
explain everything there is to know about VoIP. It will show you how to make
a small office run on Cisco VoIP using Call Manager Express and Cisco 79xx
phones.

How VoIP Works

From a network standpoint, VoIP has two main functions: call control ...

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